Bit retainer for impact tools



July 8, 1969 R. 5. MOORES, JR

BIT RETAINER FOR IMPACT TOOLS Filed Sept. 14. 1966 INVENTOR ROBERT G.MOORES, JR.

ATTORNEY United States Patent 3,454,284 BIT RETAINER FOR IMPACT TOOLSRobert G. Moores, Jr., Cockeysville, Md., assignor to The Black andDecker Manufacturing Company, Towson, Md., a corporation of MarylandFiled Sept. 14, 1966, Ser. No. 579,260 Int. Cl. B23b /22, 5/34, 31/10US. Cl. 279-191 7 Claims ABSTRACT OF THE DISCLOSURE The device disclosedherein is a portable, power operated rotary hammer adapted to impartrotation and longitudinal reciprocation to a tool bit. A novel bitretainer construction is provided to prevent the bit from pulling out ofthe tool and prevent unintended tool bit and retainer recycling orflutter.

This invention relates generally to power tools, and particularly to animproved bit retainer assembly for impact tools.

Important objects of the present invention are to provide an improvedretainer assembly for use with impact tools which is adapted to cushionboth forward and return movement of the retainer when struck by the toolbit to thereby prevent unintended tool bit and retainer recycling orflutter.

Additional objects of the present invention are to provide a tool bitretainer assembly of the above character which facilitates readyassembly and disassembly from its mounting as well as tool bit removaland replacement.

Further objects include the provision of a tool retainer assembly of theabove character which is relatively inexpensive to manufacture, ruggedin construction and reliable in use.

Other objects and advantages of the present invention will become moreapparent from a consideration of the following detailed descriptiontaken in conjunction with the drawings in which:

FIGURE 1 is a side elevational view, partly in section,

illustrating an impact tool embodying the present in-- vention;

FIGURE 2 is an enlarged sectional view of FIGURE 1 taken along the line22 thereof and showing the parts in a retracted position;

FIGURE 3 is a view similar to FIGURE 2 showing the parts in an extendedposition;

FIGURE 4 is a sectional view of FIGURE 2 taken along the line 44thereof;

FIGURE 5 is a sectional view of FIGURE 2 taken along the line 5--5thereof showing the retainer plate positioned for normal tool bit use;and

FIGURE 6 is a view similar to FIGURE 5 showing the retainer platepositioned for tool withdrawal.

Broadly described, the present invention includes, in a power operatedrotary tool, a housing, a reciprocable tool bit extending outwardly ofsaid housing, retainer plate means embracing said tool bit, meanssupporting said retainer plate upon said housing for movement toward andaway from said housing, said supporting means including closed cylindermeans having piston means slidably disposed wholly therewithin, saidpiston and closed cylinder means movable relative to each other in adirection parallel to the path of movement of said tool bit, said pistonmeans including rod means extending slidably through one end of saidclosed cylinder means and adapted to displace air within said cylindermeans during movement relative thereto in both directions, one of saidpiston 3,454,284 Patented July 8, 1969 "ice and closed cylinder meansbeing fixed to said retainer plate means and the other being fixed tosaid housing and means normally biasing said retainer plate means towardsaid housing.

Referring now more particularly to the drawings, a rotary hammer, whichis one type of tool with which the retainer assembly of the presentinvention finds use, is illustrated generally at 11 in FIGURE 1. Therotary hammer 11 is seen to include a case housing 13 having an endhousing 15 secured thereto by screws 17. An end handle and gear case 19is fixed to the case housing 13 by screws 21 and has lateral flanges 23(only one of which is shown) fixed to the case housing 13 by screws 25.The handle and gear case 19 has a conventional trigger switch 27 andline cord 29, and the handle 19 together with the housings 13, 17 may beconstructed from a die cast aluminum alloy or molded using a suitableglass fiber material as is customary in the art.

The rotary hammer is provided with a suitable power source, for example,an electric motor (not shown), positioned within the case housing 13which is adapted to impart longitudinal reciprocating movement to a toolbit 31, and, in the case of a rotary hammer, rotation about itslongitudinal axis as well. Thus, the electric motor (not shown) may havefield windings and a rotating armature connected to a piston andfloating ram by a gear and crank transmission to reciprocate the pistonand ram and hammer on the tool bit 31. For example, a construction ofthis type is illustrated and described in detail in US. Patent No.3,203,490, granted Aug. 31, 1965 to G. W. McCarty et a1. and owned bythe assignee of the present application and for a better understandingthereof reference may be made thereto.

As described above, the tool bit 31 may be rotated about itslongitudinal axis. To this end the electric motor armature (not shown)has an armature shaft (not shown) drivingly interconnected with the toolbit 31 through a transmission (not shown).

The tool bit 31 is adapted for rotation upon energization of theelectric motor (not shown) or other power source by being keyed to agear or shaft rotated by the power source. For example, the tool bit 31may have an integral hexagonal shank slidably received in acomplimentary hexagonal socket opening in a driven gear supported withinthe end housing 15 as illustrated and described in the McCarty et a1.patent referred to above. In addition, if desired, a slip clutch devicemay be integrated with the transmission to prevent undue shock andpossible injury to the tool operator and/or the transmission components.

In impact tools of this type, one of the problem areas lies incontrolling movement of the tool bit 31 should the bit be withdrawn fromcontact with the Work before the tool is turned off. It is customary inthe art to provide a spring loaded bit retainer for preventing the toolbit from pulling out of the tool housing. The bit normally operates freefrom contact with the retainer; but if the bit is withdrawn from thework, an abutment on the bit strikes the retainer and prevents the bitfrom flying out of the housing. When the bit abutment strikes theretainer, the bit and retainer move together until loading of theretainer springs overcomes the inertia force of the bit and returns thebit back into the tool housing and the retainer to its normal retractedposition. If desired, the tool operating ram is caught and held by acollet within the housing if the bit is allowed to move outwardlysufficiently far to strike the retainer. In the past, the retractingaction of the retainer springs was unimpeded so that if the ram struckthe bit with sufilcient force on a stroke after the bit was withdrawnfrom the work, the loaded retainer springs threw the bit back into thetool housing to knock the ram from its collet. The ram then strikes thepiston and rebounds against the tool bit causing it to recycle andstrike the retainer. This, in turn, causes the retainer and its springsto vibrate or flutter with reinforced vibration all of which results inpremature spring failure.

In addition to these vibrational stresses, the retainer springs aresubject to high shock forces during initial contact between the tool bitand the retainer plate which also, if left uncontrolled, results inpremature spring failure.

According to the present invention, the aforementioned problems havebeen obviated by providing a novel retainer assembly which employs amechanical spring return integrated with an air spring constructionfunctioning conjointly both to absorb the primary shock imposed on theretainer by the tool bit 31 during initial striking contact therebetweenas well as to cushion return movement of the retainer and tool bit 31 toprevent recycling of the parts after power source deenergization asdescribed above.

Turning now to FIGURES 26, the retainer assembly is shown generally at33 and is seen to include a retainer plate 35 provided with a centralopening 37 embracing a reduced diameter portion 38 of the tool bit 31.The relative diameters and axial lengths of the plate opening 37 and thetool bit portion 38 allows free rotation of the tool bit 31 and axialhammering reciprocation thereof when the bit is engaged with workwithout moving the retainer plate 35.

The retainer plate 35 is supported from the end housing by a pair ofretainer rods 39, 41 having their outer ends extending through anopening 43 and an arcuately elongated slot 45 in the plate 35 and therod inner ends are slidable in sleeve-like cylinders 47, 49,respectively, in the end housing 15. The outer ends of the rods 39, 41are threaded and receive retaining nuts 51, 53. A pair of opposedBelleville washers 55, 57 are positioned between the plate 35 andshoulders 59, 61 on the rods 39, 41, respectively, and the plate 35 isheld against each pair of washers 55, 57 by the nuts 51, 53.

The inner ends of the retainer rods 39, 41 are fashioned after pistonshaving enlarged heads 63, 65 slidably received in the sleeve cylinders47, 49, respectively. The sleeve cylinders 47, 49 in turn are positionedin bores 67, 69 formed in the outer end of the end housing 15, whichbores may be tapered at their outer ends at 68, 70 to facilitate easyinsertion and removal of the sleeve cylinders 47, 49. These sleevecylinders are held in place by a cover plate 71 fixed to the end housing15 by screws 73, which plate also serves to substantially close theouter ends of the sleeve cylinders 47, 49. The retainer rods 39, 41 arenormally retracted within the sleeve cylinders 47, 49 and seated againstwafer-like seals 75, 77 by compression springs 79, 81 caged between theenlarged heads 63, 65 and retainer rod guides 83, 85, respectively.

In use, the tool bit 31 is hammered on by the reciprocating ram (notshown) with tool bit positioned substantially as shown in FIGURE 2. Toolbit 31 is reciprocated longitudinally with a relatively small amplitudeand when engaged with the work does not contact the retainer plate 35.When the hammer is retracted from work, however, the tool bit 31 canmove longitudinally forward by force of gravity or, as is more likely,the force of the last blow struck by the reciprocating ram. The tool bit31 initially travels substantially free of movement of the retainerplate 35 even after the hammer is retracted from the work owing to thefact that the tool bit reduced diameter portion 38 has a substantiallygreater axial length than the thickness of the retainer plate 35.However, when a shoulder 79 at the inner end of the reduced diameterportion 38 of the tool bit 31 strikes the retainer plate 35, the latterthereafter moves with the tool bit 31 to substantially the positionshown in FIGURE 3 and compresses the springs 79, 81. By this time theram has contacted a split steel collet (not shown) which is provided toresiliently hold the ram stopping the hammering action thereof untiloperator pressure on the bit 31 forces ram out of the holding collet andallows reciprocation of ram to resume. When the force of the loadedcompression springs 79, 81 is sufiicient to overcome the inertia forceof the traveling bit 31, the springs retract the retainer plate 35 untilthe enlarged piston-like portions 63, 65 of the rods 39, 41 bottom inthe cylinder sleeves 47, 49 as shown in FIG- URE 2.

It will be appreciated that when the retainer rods 39, 41 move from theFIGURE 2 position upon the retainer plate 35 being engaged by the bitshoulder 89, a volume of air, which is a function of the cross-sectionalarea of the heads 63, 65 less the cross-sectional area of the rods 39,41, is displaced. This displaced air leaks past the heads 63, 65 andserves to cushion and absorb the primary shock caused by the bitshoulder 89 striking the retainer plate 35 so that the mechanicalsprings 79, 81 are not subjected to these severe forces.

When the tool bit and retainer plate 35 begin their retracting movement,a volume of air, which is a function of the cross-sectional area of therod heads 63, 65, is displaced thereby and leaks back past these heads63, 65. This prevents the energy of the compression loaded springs 79,81 from throwing the tool bit 31 back against the ram and causingrecycling and reinforced vibration fluttering of the retainer plate 35.This, in turn, alleviates severe stresses on the mechanical springs 79,81 and prevents premature failure thereof as described above.

Although the component sizes and spring strengths for the retainerassembly of the present invention can vary from one installation toanother, in one particular practical application, given for purposes ofillustration only, very satisfactory results have been achieved usingmechanical springs 79, 81 having a compressive force of about 20 lbs.per inch and constructing the retainer rods 39, 41 so that their heads63, 65 each has a total cross-sectional area of about 0.440 sq. in. anda differential cross-sectional area of about 0.330 sq. in. and whereinthe clearance between the heads 63, 65 and the sleeve cylinders 47, 49is from about 0.001 to about 0.002 in.

To remove the tool bit 31, the retainer plate 35 must be moved from theposition shown in FIGURE 5 to the position shown in FIGURE 6. Theretainer plate 35 is frictionally held in position by the Bellevillespring washers 55, 57 but a suitable blow with a soft hammer or similarmeans will change the retainer plate position. In the latter position,the tool bit 31 is positioned in a somewhat larger opening 91 than theopening 37 and which is larger than the diameter of the tool bitshoulder 89. In this position of the parts, the tool bit 31 is easilyremovable and replaceable and does not necessitate dismantling orremoving the retainer plate.

By the foregoing, there has been disclosed an improved impact toolretainer assembly calculated to fulfill the inventive objectshereinabove set forth, and while a preferred embodiment of the presentinvention has been illustrated and described in detail, variousadditions, substitutions, modifications and omissions may be madethereto without departing from the spirit of the invention asencompassed by the appended claims.

I claim:

1. In a power operated rotary tool, a housing, a reciprocable tool bitextending outwardly of said housing, retainer plate means embracing saidtool bit, means supporting said retainer plate means upon said housingfor movement toward and away from said housing, said supporting meansincluding closed cylinder means having piston means slidably disposedwholly therewithin, said piston and closed cylinder means movablerelative to each other in a direction parallel to the path of movementof said tool bit, said piston means including rod means extendingslidably through one end of said closed cylinder means and adapted todisplace air within said cylinder means during movement relative theretoin both directions, one

of said piston and closed cylinder means being fixed to said retainerplate means and the other being fixed to said housing, and meansnormally biasing said retainer plate means toward said housing.

2. A device as defined in claim 1 wherein said piston means is fixed tosaid plate means and said closed cylinder means is carried by saidhousing.

3. A device as defined in claim 1 wherein said piston and closedcylinder means includes a pair of slidably disposed piston and closedcylinder means, one on either side of said tool bit.

4. A device as defined in claim 1 wherein said biasing means includesspring means disposed within said closed cylinder means and engagingsaid piston means.

5. A device as defined in claim 2 wherein said closed cylinder meansincludes cylindrical sleeve means disposed in an opening in said housingand said piston means includes rod means fixed to said retainer plateand having an enlarged head slidable in said cylindrical sleeve means.

6. A device as defined in claim 2 wherein said one end of said closedcylinder means includes a cover plate removably secured to said housingand having opening means therethrough slidably receiving said rod means.

7. A device as defined in claim 3 wherein said tool bit has a reduceddiameter portion, said retainer plate means comprising a plate having afirst slot slightly larger than and embracing said tool bit reduceddiameter portion, a second slot in said retainer plate communicated withsaid first slot and adapted to permit free axial movement of said toolbit therethrough when aligned therewith, said retainer plate beingmovable to selectively align said first and second slots and said toolbit.

References Cited UNITED STATES PATENTS 1,240,649 9/1917 Bayles 279-l9.23,022,769 2/1962 Amundsen 27919.5 1,015,509 1/1912 Prellwitz 279-19.21,414,234 4/ 1922 Tuttle 279--19.1 1,429,808 9/1922 Tuttle 27919.11,503,932 8/ 1924 Wilhelm 279-19.! 2,045,296 6/ 1936 Fuehrer 27919.22,182,365 12/1939 Smith 279--19.1

FOREIGN PATENTS 1,078,064 3/1960 Germany.

ROBERT C. RIORDON, Primary Examiner.

' J. C. PETERS, Assistant Examiner.

